When chlorine-containing resin compositions are subjected to thermoforming or when the molded articles of said compositions are exposed to high temperatures for a long period of time, they give rise to thermal degradation accompanied by dehydrochlorination, whereby discoloration and/or deterioration in physical properties of the resin are caused. In the case of the molded articles, the commercial value is reduced significantly. Hence, it has been conventional to add to chlorine-containing resins a stabilizer which is a combination of a salt of a carboxylic acid with a metal such as barium, zinc or the like with an organic ester of phosphorous acid, a phenolic antioxidant or the like to stabilize the chlorine-containing resins
Molded articles obtained from such stabilized chlorine-containing resin compositions have recently been used in large quantities as interior parts of automobiles. In the case of a molded article of a chlorine-containing resin composition with a soft resin formulation, a urethane is injected into the interior of the molded article or laminated onto the back side of the molded article and foamed for the purpose of making automobiles lighter, improving the impact resilience and hand of the molded article and enhancing the safety of drivers. The molded articles thus obtained are utilized as interior parts of automobiles. Such interior parts of automobiles have been produced by subjecting a resin composition to calendering or extrusion to obtain a sheet and then subjecting the sheet to vacuum forming. Therefore, the thermoforming conditions in this production are substantially the same as those in the production of general molded articles, and accordingly, the chlorine-containing resin compositions containing the above-mentioned known combination of stabilizing components are thermally stable enough under the thermoforming conditions. However, it has been difficult to form a complicated grain leather pattern on the surface of the above molded articles and even if the pattern can be formed the hand of the molded articles obtained is not satisfactory. Therefore, it has been designed to form a complicated grain leather pattern having an improved hand.
Under such circumstances, powder molding methods have been employed in recent years to realize said improvement. The powder molding methods are disclosed in, for example, Japanese Patent Application Kokai No. 60-161451, Japanese Patent Application Kokai No. 61-91238 and U.S. Pat. No. 4,659,764.
In these prior art references, a molding method is adopted which comprises adding, to a chlorinecontaining resin, a stabilizer, a platicizer, a pigment, etc., mixing them thoroughly with heating (so-called dry-blending) to obtain a resin composition in the powder form, sprinkling the powder form resin composition on a metal mold at a high temperature of 200-280.degree. C by rotational powder molding or powder slush molding to fuse the powder particles, and cooling the fused product to obtain a molded article. The molded article for use as an interior part of automobiles obtained by the above powder molding has the advantage that the outermost layer thereof has a precise, complex, calm, leather-like pattern and hand. However, there are such problems that since, in the powder molding, a chlorine-containing resin composition in the powder form is sprinkled on a metal mold at a high temperature to fuse the powder particles without being beforehand subjected to kneading and gelation, a resin composition consisting of a chlorine-containing resin and a conventional amount of a conventional stabilizer tends to be thermally degraded with discoloration when it is subjected to the powder molding. Furthermore, there is a further problem that when the metal mold is repeatedly used in the powder molding of the above resin composition the molding surface of the metal mold is stained. In addition, the interior parts obtained by subjecting the molded article to integral molding with a urethane as a secondary processing are discolored when they are exposed to a high temperature of 80-130.degree. C. for 300 hours or more, resulting in deterioration of quality.
In order to overcome the above severe thermal conditions in the powder molding, thermal stabilization of chlorine-containing resin with various stabilizers has so far been proposed. However, no sufficient stabilization is obtained and an improvement thereof has been desired.